Downhole instruments or tools for subterranean wells are lowered down a well bore and operated in a subterranean reservoir to measure, for example, formation characteristics such as bottom hole pressures and temperatures as a function of time, and to perform many other measuring, control and operational tasks in a well.
Tools of this type are typically lowered on a conductive wire line. The wire line is formed of coiled metal tubing ranging from 1/8"-1/2" in diameter, within which one or more conductors capable of transmitting a signal and/or power are located. These conductors can be insulated conductor wires, optical fibers or any other conductor capable of transmitting signals and/or power to or from a downhole location.
The use of electrical conductors within a wire line is known, and are described in U.S. Pat. Nos. 5,122,209 and 5,495,755, both of which are incorporated herein by reference. Because wire line tubing of this type comes in lengths greater than 10,000 feet, up to and longer than 20,000 feet, there has been difficulty in inserting the conductor in such lengths of tubing.
In the past, as described in U.S. Pat. No. 5,122,209, a plurality of electrical conductors have been formed within the coiled tubing by feeding a flat metal strip and the conductors simultaneously through a series of tube-forming dies, and then forming the tubing with the conductors in it by welding the elongated edges of the metal strip around the conductors. Such methods have proved useful in the past, but problems have arisen.
For example, fabrication of a wire-in-a-tube by using this method often resulted in an imperfection in the tube before the entire length of product is completed, which cannot be repaired. This adds significant cost to the manufacturing process because of the high scrap rate.
Moreover, with the advent of much deeper wells, those 16,000 feet and deeper, relatively small diameter tubing formed of a high strength material such as INCOLOY 825.RTM., which has a relatively thick wall that is useful in such wells, cannot be formed with a conductor in it. Annealing the tubing and drawing it down in size are necessary for eliminating microscopic circumferential cracks in the weld and increasing the strength due to work hardening of the material. These steps cannot be performed with a conductor in the tubing.
Thus, there is a need for a method of making conductive wire line, especially those useful in today's deep wells, which eliminates these problems.